Different carbon treatments for steel slag powder and their subsequent effects on properties of cement-based materials

Abstract

In order to fill the research gap of CO 2 -fixing cementitious materials, and to deal with China's dual-carbon goal, first to use bacteria and steel slag powder to fix CO 2 . The paper using untreated steel slag powder as control group, different CO 2 -fixing steel slag powder are compared, they are CO 2 treated steel slag and bacteria-CO 2 treated steel slag. The XRF and XRD results shows that the physicochemical properties of steel slag powder with different treatments are significantly different. Because the chemical composition and particle surface properties of steel slag powder are changed in the CO 2 fixing process due to the reactions. There are calcium carbonates formed in steel slag powder when cured by CO 2 from cement kiln tail gas. The SEM images show that the surface of steel slag powder has defects. Steel slag with bacteria will produce more calcium carbonates and its surface has more defects. Therefore, it will have an impact on the cement-based material fresh paste workability and hardened paste properties. The results of the fresh paste workability show that, the surface defects of steel slag powder have an adverse impact on the workability, because the defects increase the internal friction between particles. The results of hardened paste strength show that the cement-based materials mixed with SSLP-BC has the better mechanical properties. The XRD, FTIR , SEM, 1 H NMR and X-CT results of hardened paste show that, the microstructure of cement-based materials mixed with SSLP-BC is denser. This may be caused by the nucleation of bacteria and calcium carbonate. Moreover, calcium carbonate may play an important role in hydration process , there is carboaluminates formed in the hardened paste that containing calcium carbonate, and it is beneficial for mechanical properties. Therefore, steel slag after bacteria-CO 2 treated can used as SCM , it has better social and environmental benefits.